This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 10-037613, filed Feb. 19, 1998; and No. 10-037614, filed Feb. 19, 1998, the entire contents of which are incorporated herein by reference.
The present invention relates to a method for performing sterilizing treatment on such a plastic container as a PET bottle and the like. In particular, the present invention relates to a method and an apparatus for performing heating and sterilizing treatment on an inner face of a plastic container having a low heat-resistance securely without thermally deforming the same.
Conventionally, the so-called PET bottle is widely used as a plastic container filled with a drink or the like. In this case, before a drink is filled in such a PET bottle, sterilizing treatment must be performed on an inner face of the bottle. Incidentally, as the sterilizing treatment for a drink container, there are various treatments such as sterilization which dies out bacteria completely in a strict sense, sterilization which reduces or incapacitates bacteria down to a required level, and the like. In this specification, treatments including all of these treatments are referred to as sterilizing treatments.
As such a sterilizing treatment, there is one where heating and sterilizing treatment is performed by jetting hot water on to an inner face of a PET bottle. Such a heating and sterilizing treatment is generally applied alone or in combination with another sterilizing treatment such as jetting of ozone water or the like. In such a heating and sterilizing treatment, there are advantages such as simple steps, secure treatment and the like, but there are the following problems to be solved.
The first problem is that heat resistance is required for a container to be subjected to sterilizing treatment. In order to obtain effect of sterilizing treatment, it is necessary to jet hot water having a temperature of 65 to 70xc2x0 C. or more. However, such a high temperature exceeds a heat resistance temperature of resin material for a container and deformation occurs in the container due to heat. Accordingly, for example, in a case that heating and sterilizing treatment is performed by jetting hot water on an inner face of a PET bottle, it is necessary to use a PET bottle using heat resistance material. For this reason, cost for a container is increased and kind of containers which can be subjected to sterilizing treatment is limited.
Also, the second problem is related to a temperature range of hot water and safety. When the temperature of this jetting hot water becomes higher, the effect of the sterilizing treatment becomes higher, so that it is preferable that the temperature of the hot water is higher. However, since there are portions where pressure of hot water is lowered locally inside pipes or valve apparatuses for supplying the hot water, when the temperature of the hot water becomes about 90xc2x0 C. or more, there is a possibility that boiling occurs at low pressure generating portions in the pipes or the valve apparatuses, so that the temperature of the hot water must be maintained at about 90xc2x0 C. or less. Also, though it is considered that the hot water is pressurized and supplied thereby preventing boiling in pipes such as the above, hot water having a high pressure and a high temperature is not preferable in view of safety because there is a high risk that, if the pipe or the like is broken, hot water is scattered far and it attaches to a human body to burn him/her.
Also, the third problem is related to energy cost for producing the above hot water. In this manner, since the hot water which has been jetted on the inner face of the container is disposed as it is, energy cost for producing a large amount of hot water becomes high.
Furthermore, the fourth problem is a problem where hot water is jetted uniformly on the inner surface of the container. When a container to be subjected to sterilizing treatment has a complicated shape, it becomes difficult to jet hot water uniformly and thoroughly on the inner surface thereof. Also, even when the entire shape of a container is simple, for example, in the case of a PET bottle, there are many bottles where a number of ribs or recess/projection portions are formed on wall faces in order to increase rigidity of a bottle, improve design matter, and the like. There is a possibility that portions where jetting of hot water or falling-down thereof is obstructed are formed on these ribs or recess/projection portions, so that reliability of sterilizing treatment may be injured in some cases. Also, recently, a PET bottle which is crushed to decrease its volume at a time of disposal has been required. In such a bottle, it is anticipated that wall faces of the bottle are constituted in a complicated manner in order to facilitate crushing. In such a case, there is a possibility that portions of the bottle on which hot water is not jetted sufficiently occur.
In order to solve the above first problem, there has been recently proposed a method where hot water is jetted on an inner face of a PET bottle and simultaneously cooling water is jetted on an outer face of the bottle to cool the bottle wall face so that the bottle is prevented from deforming due to heat. According to such a method, since the temperature of the bottle wall face is prevented from increasing, such an effect can be obtained that it is made possible to perform heating and sterilizing treatment of hot water jetting even on an anti-heat resistant bottle.
However, it is necessary to suppress the temperature of the jetting hot water to 90xc2x0 C. or less in order to prevent boiling or the like in pipes in the above manner, and there is a limitation in the temperature of the hot water. Also, the heat transfer from the hot water to the bottle wall face is a heat transfer due to impingement of jet flow of fluid to wall face, so-called impinge heat transfer, and it is a heat transfer system having a highest efficiency as a heat transfer system between fluid and wall face. Accordingly, since a large amount of heat is transferred from hot water to bottle wall face, the effect of the prevention of temperature rising on the wall face becomes insufficient even if the outer face of the bottle is being cooled. For this reason, for example, in a case of an anti-heat resistant PET bottle, the temperature of the hot water must be set to a temperature lower that the above 90xc2x0 C. in order to prevent thermal deformation of the bottle. Accordingly, the efficiency or reliability of the heating and sterilizing treatment is lowered.
Also, in the above method, there is an effect that deformation of a container due to heat can be prevented in the above manner, but the above-mentioned second and fourth problems can not be solved essentially.
In order to solve the problems as mentioned above, a method is considered that an outer face of a bottle is cooled with cooling water or the like and steam is jetted on to an inner face of the bottle so that heating and sterilizing treatment is performed. Steam has a heat capacity smaller than that of hot water, so that only an inner face portion of a wall face of a bottle is heated to a high temperature but the heat amount transferred to the wall face is small. For this reason, the temperature of an outside of the wall face of the bottle is suppressed to a low temperature so that heat deformation of the bottle can be prevented effectively. Also, since there occurs no boiling in pipes or the like, the temperature of steam can be made higher than that of hot water and heating and sterilizing treatment can be performed more effectively. Also, since steam has a high fluid property and it is not affected by gravity, even when the shape of a bottle is complicated, steam contacts with an inner face of the bottle uniformly so that it is made possible to perform heating and sterilizing treatment securely.
By the way, the steam which has been jetted inside a bottle is circulated inside the bottle and exhausted from a mouth portion. Since the heat capacity of the steam is small, as mentioned above, the temperature of the steam is lowered during the circulation inside the bottle, and the steam whose temperature has been lowered in this manner is exhausted through the mouth portion, so that the temperature of the mouth portion is not increased sufficiently in some cases. Such a drawback is easy to occur when the content volume of a PET bottle is large.
The present invention has been achieved in view of the above circumstances, and it is to provide a method for performing sterilizing treatment on a plastic container which has a high safety and can reduce cost, which can perform heating and sterilizing treatment on an inner face of a plastic container having a relatively low heat resistance effectively and securely, and which can prevent the container from deforming due to heat effectively.
Also, the present invention is to provide an apparatus for performing sterilizing treatment on a plastic container, which can perform heating and sterilizing treatment on a plastic container on an inner face of a plastic container having a relatively low heat resistance effectively and securely and which can heat the inner face of the container up to a predetermined temperature more uniformly.
In order to solve the above problems, the method of the present invention is a method for performing sterilizing treatment on a container made of plastic material comprising the steps of: inserting a steam jetting nozzle into a mouth portion of a container to be subjected to sterilizing treatment with a clearance formed between the nozzle and an inner face of the mouth portion; jetting steam into the container from the steam jetting nozzle and circulating the jetted steam in the container to exhaust the steam from the clearance between the steam jetting nozzle and the inner face of the mouth portion; and supplying cooling medium to an outer face of the container simultaneously with the step of jetting steam to cooling a wall face of the container.
Accordingly, the inner face of the wall face of the container is heated and sterilized with steam jetted and the outer face of the wall face is cooled with cooling medium, and the heat capacity of steam is smaller than that of hot water and a heat amount which is transferred to a wall face of the container is small, so that the temperature rising of the wall face of the container is suppressed to be low. Therefore, even in a case of a container having a low heat resistance, steam with a high temperature is jetted so that heating and sterilizing treatment can be performed securely.
Also, an embodiment of the method of the present invention is characterized in that the temperature of steam jetted from the steam jetting nozzle is 95xc2x0 C. or more. Accordingly, heating and sterilizing treatment can be performed more securely and more effectively, and the amount of heat transfer from the steam to the container wall face is small, so that the temperature of the container wall face is suppressed to be low and heat deformation or the like is prevented from occurring.
Also, in an embodiment of the method of the present invention, the step of inserting the steam jetting nozzle into the mouth portion of the container is to insert the steam jetting nozzle from the underside of the container into the mouth portion of container which is put in an inverted state where the mouth portion is directed downward, and the step of jetting steam is to jet steam into container upward towards the bottom thereof to circulate the steam along the inner face of the wall face of the container and exhaust the circulated steam from the mouth portion of the container. Accordingly, water which has been condensed on the container inner wall is caused to flow down due to gravity so that the water can be exhausted together with steam from the mouth portion effectively and the effect of sterilizing treatment is high. Also, in a case that, after the sterilizing treatment, another sterilizing treatment is performed, the condensed water is prevented from obstructing the another sterilizing treatment.
Also, an embodiment of the method of the present invention is characterized by further comprising the step of directly jetting steam on the inner face of the mouth portion of the container. Since steam which has been circulated in the container passes through the inner face of the mouth portion, the steam with a reduced temperature contacts with the inner face so that the effect of the heating and sterilizing treatment tends to lower. However, by jetting stream directly to the mouth portion, heating and sterilizing treatment can be performed on the inner face of the mouth portion more securely.
Also, an embodiment of the method of the present invention is characterized by further comprising the step of jetting steam on an outer face of the mouth portion of the container. Accordingly, simultaneously with the heating and sterilizing treatment on the inner face of the mouth, the outer face of the mouth is also subjected to heating and sterilizing treatment, so that a possibility that the inside of the container is contaminated secondarily after the heating and sterilizing treatment can be prevented securely.
Also,an embodiment of the method of the present invention is characterized in that the cooling medium supplied to the outer face of the container is cooling water. Accordingly, the outer face of the container can be cooled easily and securely.
Also, an embodiment of the method of the present invention is characterized in that the cooling medium supplied to the outer face of the container is cooling wind. Accordingly, the outer face of the container can be cooled by an equipment having a simple structure, and there is no possibility that such a problem as contamination in the container or the like occurs due to cooling water, so that more secure sterilizing treatment can be performed.
Also, an embodiment of the present invention is characterized in that steam jetted form the steam jetting nozzle into the container is pure water steam where impurities are removed from steam supplied from a boiler. Accordingly, there is no possibility that the inside of the container is contaminated secondarily by the steam and secure sterilizing treatment can be performed.
Also, an embodiment of the method of the present invention is characterized in that steam jetted from the steam jetting nozzle into the container is pure water steam where impurities are removed from steam supplied from a boiler. Accordingly, there is no possibility that the inside of the container is contaminated secondarily by the steam and secure sterilizing treatment can be performed.
Also, in order to achieve the above object, an apparatus of the present invention is characterized by comprising a holding mechanism for holding a container to be subjected to sterilizing treatment, a steam jetting nozzle inserted into a mouth portion of the container, and a steam supplying mechanism for supplying steam to the steam jetting nozzle to jet the steam from the nozzle into the container, in which the diameter of the steam jetting nozzle is smaller than the inner diameter of the mouth portion of the container, a clearance is formed between an inner peripheral face of the mouth portion and an outer peripheral face of the steam jetting nozzle, and a side nozzle hole which is opposed to the inner peripheral face of the mouth portion of the container for jetting steam to the inner peripheral face of the mouth portion is formed in the steam jetting nozzle so as to open on an outer peripheral face thereof.
Accordingly, since the outer face of the container is cooled by cooling medium, the container is prevented from heat-deforming, and only the inner face thereof is heated up to a high temperature by steam so that heating and sterilizing treatment can be performed effectively and efficiently. Also, since the heat capacity of steam is small, the amount of heat transferred from the steam to a wall face of the container becomes small, the temperature rising of the wall face is small, and the heat deformation of the container is prevented more effectively. Also, since the fluid property of steam is large and steam is not affected by gravity, the inner face of the container can be caused to contact with steam uniformly and everywhere, even when the shape of the container is complicated. Also, since boiling does not occur in pipes or the like, there is no limitation in the temperature of the steam and a safety is high even when breaking of a pipe or the like occurs.
Also, the steam jetted into the container is exhausted from the clearance between the mouth portion and the nozzle after circulated in the container. In this case, there is a case that the temperature of the steam passing through the mouth portion is lowered so that the temperature rising of an inner face of the mouth portion becomes insufficient, but since steam is jetted directly on to the inner peripheral face of the mouth portion from the side nozzle hole on the outer periphery of the steam jetting nozzle, the mouth portion can sufficiently be heated.
Also, in an embodiment of the apparatus of the present invention, the holding mechanism is provided with a grasping mechanism for grasping the mouth portion of the container, and the grasping mechanism is structured so as to invert the container while grasping the mouth portion of the container to maintain the container in a state where the container is inverted such that the mouth portion of the container is directed downwardly.
Accordingly, hot water condensed on the inner face of the container flows down due to gravity and it is exhausted from the mouth portion together with steam so that the condensed water does not remain in the container.
Also, an embodiment of the apparatus of the present invention is characterized by comprising a mouth portion outer face nozzle for jetting steam towards an outer face of the mouth portion of the container. Accordingly, since heating and sterilizing treatment is also performed on the outer face of the mouth portion, a possibility that secondary contamination occurs inside the container is prevented.
Also, in an embodiment of the apparatus of the present invention, an opening/closing valve for shutting off steam supplied to the steam jetting nozzle is provided in the steam supplying mechanism, and a bypass valve for supplying a predetermined amount of steam to the steam jetting mechanism even when the opening/closing valve is in a closed state is provided so as to bypass the opening/closing valve in parallel therewith. Accordingly, even when the opening/closing valve is closed to stop jetting of steam, steam is supplied to the nozzle through the bypass valve little by little so that contamination in the nozzle is prevented.
Also, an embodiment of the apparatus of the present invention is characterized in that an opening/closing valve for shutting off steam supplied to the steam jetting nozzle is provided in the steam supplying mechanism and a bypass passage for supplying steam to the steam jetting nozzle even when the opening/closing valve is in a closed state is formed inside the opening/closing valve. Accordingly, like the above embodiment, even when the opening/closing valve is closed to stop jetting of steam, steam is supplied to the nozzle through the bypass valve little by little so that contamination in the nozzle is prevented.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.